ok i have a 2012 Sultura Evo 905 Merida i was thinking of upgrading to DI2 Ultegra but after chating to a few LBS i have decided to upgrade my rims instead as i would prob get more gain from it.I don't race just ride for fitness, i rode with others & we are very competitive within our group rides so if this helps me a little then great i have Fulcrum Comp rims atm (standard fitment) & am thinking of up grading to RS80 C24 carbons can get them for $600 is this the right place to upgrade ?

From the limited understanding I have of Fulcrums, the Comp is roughly equivalent to Mavic Aksiums or Shimano R500s (so a step above the very common entry level Shimano hubs/Alex rims wheelsets), if that is the case then you will notice a BIG difference going to the RS80s. I have a set that has seen at least 3,000kms so far, no issues at all so far, they feel much better for accelerating and climbing, and a lot stiffer and more 'direct'.I wouldn't mind getting some deeper rims though for going fast on the flat.

When man invented the bicycle he reached the peak of his attainments- Elizabeth West.

Weight vs. aero. Deeper rims are heavier, no escaping that fact, because more material has to go into building them. As a result, they don't climb as well, because the inertia of extra rotating mass requires more effort to keep moving upward, which works against you. However, on the flat the weight is less of a concern, as the deeper profile makes a smoother hole through the air, and once up to speed will maintain that speed better. On the other side, deep rims can be a handful in strong crosswinds, especially with a light rider on board.

Pick your rims to suit your riding. If you're doing a lot of hill work, go shallower. If you're mainly a flat rider, and not overly bothered by crosswinds, go deeper. If you do a bit of everything, or are a flyweight who gets chucked around a lot by strong winds, play the middle ground & go the 35s.

$600 for RS80's is a little steep, have a look around but I'm pretty sure I've seen them online for ~$500. They're great wheels, and give surprisingly low drag numbers (similar to other brands dodgy aero wheels) for the depth.

In summary, wheels account for almost 10% of the total power required to race your bike and the dominant factor in wheel performance is aerodynamics. Wheel mass is a second order effect (nearly 10 times less significant) and wheel inertia is a third order effect (nearly 100 times less significant). The best wheels in terms of performance are the ones that are lightweight, aerodynamic, don’t rub brake pads and are strong enough to get you to the finish line. The problem with these high performance wheels, though, is that they sacrifice on the other two key variables important in wheel selection: durability and price. High performance wheels are neither durable nor cheap. Nothing is ever easy, is it?

Is there anything in particular with your wheels that you don't like? If you are not racing and just riding for fun, just keep riding. You don't necessarily need to upgrade you wheels but if you want to then go ahead.

well i got the new ultegra crankset fitted & they said you will feel the difference in riding & i sort of though year whatever, but i can the bike feels more responsive when i pedal hard & i seam to be able to keep a higher cadence for longer is this all in my head or is this the effect a lighter stiffer crankset offers ?

prob should have mentioned i went from BB30 FSA cranks to these Ultegra not sure of the arm length of the FGSA but these ultegra i chose 172,5 mm , we used a scram press in insert & an ultegra bottom bracket , feels so smooth now to

As others have said, deaper rims are heaver and therefore you need more energy to spin the rim and if your not going in a straight line (not stopping at traffic lights) for long periods then you might get away with the aero affects of the deeper rims, I would go for a lighter shallower rim so i don't waste energy spinning the rim up to speed. Alot of cheaper carbon rims are actually carbon/alloy and the carbon is only a thin overlay to creat the deep look and aero affect, but mostly just adding unecessary weight for no reason.